Everest Pyramid GAW Station: a new laboratory for atmospheric sciences and climate studies in Himalaya. By Paolo Bonasoni

The negative effects of climate change are mostly observed in developing Countries, with particular emphasis on Asia. As in other parts of the world, this area is under a double threat: the first one, at a larger scale, is related to global warming as a result of increasing greenhouse gas emissions to which the Asian continent contributes significantly, while the second one is connected to climate change at the regional scale, influenced by the high aerosol - black carbon in the first place - and ozone concentrations in the atmosphere, causing widespread clouds called "Atmospheric Brown Clouds (ABCs)". These ABCs are vertically and horizontally spread and, depending on weather conditions and lifetime of the pollutants (usually between few days and few weeks), they can reach a thickness of up to 3-4 kilometres and a spatial extension of hundreds of square kilometres. By absorbing and reflecting the solar radiation, these clouds modify climate, atmospheric circulation and the water cycle, influencing agricultural production, which sustains the local population.
This is also one of the reasons why the Himalayan region becomes a strategic area for monitoring of the atmosphere, since here are located the most extended extra-polar glaciers providing water resources for more than a billion people. However, only little information on the atmospheric composition in this area is available, especially for the southern part, more directly influenced by ABCs -.
The Everest-Pyramid station, located at 5079 m asl was established for filling this gap of information and was supported through the projects "Station of High Altitude for Research on the Environment - SHARE" (by Ev-K2-CNR) and "Atmospheric Brown Cloud" ABC (by UNEP).
This laboratory was developed in Bologna during Autumn 2005 at the ISAC CNR, in collaboration with a group of the French CNRS. The whole instrumentation was operated for a period of two weeks, also to check the data acquisition and control and information transmission systems.
The container was then installed in the Himalayan Khumbu valley (Nepal) at the beginning of 2006, and continuous measurements of chemical, physical and optical aerosols properties, as well as atmospheric optical thickness, surface ozone, halogenated compounds and meteorological measurements were started. The power needed to carry out the experimental activity is provided by 96 photovoltaic panels with 120 electric storage cells, which ensure the power 24 hours a day, 365 days a year. A satellite connection allows the remote control of the instrumentation and the data access in real time. Every year CNR, CNRS and Ev-K2-CNR researchers visit the site to check the instruments for maintenance and the in situ calibrations.
The first results obtained so far show that the atmospheric composition in this area can be influenced both by air masses from the higher troposphere and the stratosphere and by transport of pollutants at the local, regional and continental scales. A high fraction of carbonaceous materials was found in the aerosol PM10 collected, while the presences of mineral aerosol characterize the transport of air masses from desert areas.
The atmospheric composition in the Himalayan area is strongly influenced by the monsoon seasonal circulation. During the dry season and the pre- and post- monsoon periods, mountain breezes favour the transport to high elevations of pollutants coming from the low layers of the Khumbu valley and the southern Nepal, regions often affected by the presence of ABCs. Even during the monsoon season, when the atmospheric compounds measured exhibit typical baseline concentrations, episodes of pollution were observed, also in connection with transport of air masses from South Asia (Nepal, India, Pakistan).
These first studies confirm that high concentrations of pollutants (aerosol and trace gases) can reach also the highest Earth summits, thus bringing directly and indirectly perturbation on once considered uncontaminated areas.